When her mother, Yocheved, put Moses in the basket and the basket in the Nile, Miriam watched after the basket, to make sure that her baby brother would be safe.
When Pharaoh’s daughter found the basket, Miriam went to Pharaoh’s daughter and told her that Miriam would help her find a wet nurse for the baby. Miriam went for her mother to take care of her baby brother.
We don’t know much else about Miriam until Moses comes back to Egypt. At the sea, after the crossing, and after Moses sang the great Song at the Sea, Miriam took out her musical instruments and began to lead the people in a dance of celebration.
Miriam appears again as a central character in one of the rebellions against Moses in the desert.
In the desert, Miriam is the person who always found water for the people. Some say it is because of the time when she watched her baby brother in the water of the Nile.
When Miriam dies in the desert, the people can’t find water, and Moses hits the rock, making HaShem angry.